Process and arrangement for producing dose profiles for the fabrication of structured surfaces

ABSTRACT

The object of a process and an arrangement for producing dose profiles for the fabrication of structured surfaces with a beam which is used for exposure and is directed on the surface consists in arranging the surface irradiation in such a way that the processing times and material outlay required for fabrication of micro-lenses and micro-lens arrays can be substantially reduced. According to the invention, the beam has at least one shaped region in cross section, which shaped region is movable relative to the surface and whose extent in the movement direction of the relative movement, in combination with the velocity of the relative movement, determines the dose. Effective lithographic fabrication of lens structures, in particular micro-lenses and micro-lens arrays, can be realized with the invention.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The invention is directed to a process and an arrangement for producingdose profiles for the fabrication of structured surfaces with a beamwhich is used for exposure and is directed on the surface.

b) Description of the Related Art

Devices and processes employing the technique of variable dose writingto fabricate surface profiles for electron-beam lithography andphotolithography are known (T. Fujita, H. Nishihara, J. Kayama, "Blazedgrating and Fresnel lenses fabricated by electron-beam lithography",Opt. Lett. 7 (1982) 12, p. 578; M. Haruna, M. Takahishi, K.Wakahayhashi, H. Nishihara, "Laser beam lithographed Micro-Fresnellenses", Applied Optics/Vol. 29, No. 34/1 December 1990).

The fact that the dissolve rate of a radiation-sensitive resist in thedeveloper bath can be predetermined by the radiation dose introduced inthe resist is made use of. Accordingly, it is possible to design thelateral radiation dose distribution in such a way that the desiredsurface profile is obtained after a certain period of time followingdevelopment. FIG. 14 illustrates this procedure schematically.

However, the high cost of the facilities for producing the dose profilesrequired for this process poses problems, since the systems which havebeen used up to now, such as electron-beam writing devices or laserpattern generators, are physically large and very expensive. Further,very long processing times are necessary for extended surface profiles.The fabrication of micro-lenses and micro-lens arrays especially ishighly time-consuming. Further, the amounts of data needed to write therequired dose profiles are sometimes enormous, requiring a correspondingexpenditure on computer technology.

OBJECT AND SUMMARY OF THE INVENTION

It is the object of the primary present invention to arrange the surfaceirradiation in such a way that the processing times and material outlayrequired for fabrication of micro-lenses and micro-lens arrays can besubstantially reduced.

This object is met, according to the invention, by a process forproducing dose profiles for the fabrication of structured surfaces witha beam used for exposure and directed on the surface, in that the beamhas at least one shaped region in cross section, which shaped region ismovable relative to the surface and whose extent in the movementdirection of the relative movement, in combination with the velocity ofthe relative movement, determines the dose.

The relative movement is effected in at least one of two directionswhich are inclined at an angle relative to one another. The angle isadvisably 90°, but may also diverge from 90°.

Parallel adjacent exposures are produced in the direction of relativemovement for fabricating the lens array. It is also possible to use arotating movement as relative movement.

Further, the subject of the invention is an optical arrangement forproducing dose profiles for the fabrication of structured surfaces witha beam used for exposure and directed on the surface, in which a deviceis provided for shaping the cross section of the beam, which devicegenerates at least one shaped region which is movable relative to thesurface and whose extent in the direction of the relative movement, incombination with the velocity of the relative movement, determines thedose.

The device for shaping the cross section of the beam is advantageously adiaphragm whose aperture in the movement direction, in combination withthe velocity of the relative movement, determines the dose.

The diaphragm can be a multiple diaphragm in which the individualdiaphragms are arranged one behind the other in the movement direction,and the aperture of each individual diaphragm in the direction ofrelative movement determines the dose in combination with the velocityof the relative movement.

Piezo-actuators can be connected with the multiple diaphragm to producethe relative movement which substantially corresponds to the distancebetween the individual diaphragms in the movement direction.

The diaphragm aperture advantageously has a rim formed of a straightline and a parabola, wherein the parabola, whose axis of symmetry isdirected in the movement direction, connects two points on the straightline normal to the movement direction.

Dose profiles suitable for fabricating concave Fresnel structures can beproduced when at least one rectangular shadow element is placed in adiaphragm aperture having such a rim, one side of the rectangular shadowelement coinciding with the straight line and the opposite sidecontacting the parabola by its end points. In the regions left open bythe shadow element the edges normal to the movement direction areadvantageously situated at a common border.

The diaphragm aperture can also have a rim formed of two parabolas,wherein the parabolas, which have a common axis of symmetry oriented inthe movement direction, are constructed so as to be convex in themovement direction and in the opposite direction and have commonintersection points lying on a straight line normal to the movementdirection.

Diaphragms whose aperture is a portion within a rectangular rim leftopen by a shadow element are used for producing convex structures,wherein a pair of rim sides has sides extending in a direction normal tothe movement direction.

Convex cylindrical lenses are formed by dose profiles produced by adiaphragm aperture in which one of the sides normal to the movementdirection coincides with a straight edge of the shadow element, whoseother edge is a parabola whose axis of symmetry in the movementdirection connects two points on the straight edge.

For convex Fresnel lenses, the shadow element should be formed ofpartial elements remaining after at least one rectangular portion isremoved from a surface enclosed by a straight line and a parabola,wherein the parabola, whose axis of symmetry is oriented in the movementdirection, connects two points on the straight line normal to themovement direction. One side of the rectangular portion coincides withthe straight line, while the end points of the opposite side contact theparabola.

Finally, the partial elements are so disposed that their straight edgesnormal to the movement direction are located at one of the sides of therectangular rim which are normal to the movement direction.

Diaphragms having an aperture corresponding to a fight triangle, one ofwhose legs is directed in the movement direction, may also be used. Itis also possible to use an aperture shaped like an isosceles trianglewhose vertex formed by the equal sides is directed in the movementdirection.

Adjusting slides are advantageously provided for adjusting the shape ormagnitude of the diaphragm.

A display screen which directly projects the shaped region can also beused for shaping the cross section of the beam. The shape of the regiongenerated by the display screen corresponds to the shapes generated bythe diaphragms.

The invention is explained more fully in the following with reference tothe schematic drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows an arrangement, according to the invention, for producingstructured surfaces;

FIG. 2 is a basic diagram for the process according to the invention;

FIG. 3a shows a diaphragm with a convex parabola on one side in themovement direction;

FIG. 3b shows a diaphragm with a convex parabola on both sides in themovement direction;

FIG. 3c shows a multiple diaphragm formed of individual diaphragmsaccording to FIG. 3a;

FIGS. 4a-c show parabolic diaphragms and structures produced therewith;

FIGS. 5a-c show parabolic diaphragms and structures produced therewith;

FIGS. 6a-c show a diaphragm shape and Fresnel structures fabricatedtherewith;

FIG. 6d shows the production of the diaphragm shape according to FIG.6a;

FIGS. 7a-c show a diaphragm shape and Fresnel structures fabricatedtherewith;

FIG. 7d shows the production of the diaphragm shape according to FIG.7a;

FIGS. 8a-c show a wedge-shaped diaphragm and structures producedtherewith;

FIGS. 9a-c show a triangular diaphragm and structures producedtherewith;

FIGS. 10a, b show diaphragms with variable geometry;

FIG. 11 shows a schematic arrangement for parallel production ofstructured surfaces;

FIG. 12 shows a schematic arrangement for the fabrication of roundFresnel lenses;

FIG. 13 shows a section from a round Fresnel lens;

FIG. 14 shows the basic procedure in the production of surface profileswith variable doses;

FIGS. 15a, b show a simple meandering movement and structures which canbe produced therewith; and

FIGS. 16a, b show an intersecting meandering movement and structureswhich can be produced therewith.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The arrangement according to FIG. 1 contains the following componentsarranged one after the other in the radiating direction: a light source1 with condenser, as source of radiation; a diaphragm 2 as beam shapingdevice; an objective 3 as imaging optical system; and an objectcontaining on a substrate 4 a surface in the form of a resist layer 5which is to be structured. The object is attached to an X-Y positioningtable 6. The diaphragms 2 can be permanently installed or exchangeable.An electron source, X-ray source or ion source can also be used asradiation source.

According to FIG. 2, a bundle of light 7 emanating from the light source1 is so shaped in cross section by the diaphragm 2 that a region 8 isformed separate from the remaining cross section. The shaped region 8can be moved relative to the surface to be structured by varioustechnical steps familiar to one skilled in the art. For example, theobject can be moved by means of the positioning table 6 or the lightbundle 7 can be moved jointly with the beam shaping device or bothmovements can be carried out. It is also possible to produce therelative movement of the region 8 only by linear displacement of thediaphragm 2 or by producing a rotational relative movement around avertical axis Z--Z directed parallel to the axis of the light bundle 7.

In all constructions the shape of the diaphragm depends upon thedirection of the relative movement, since the aperture in the movementdirection, together with the velocity of the relative movement,determines the dose to which the object is exposed.

In most cases, the intensity distribution over region 8 is homogeneous.However, for achieving certain results, it is also possible to designthe intensity distribution over region 8 with a defined inhomogeneity.

The imaging of the shaped region produced by the imaging optical systemmay be either sharp or unfocussed. The latter results in more uniformprofiles when the blurriness is located in the direction of the relativemovement, e.g., by using a cylindrical lens, i.e., requirements for theaccuracy of the relative movement decrease. The magnitude of therelative movement can also be reduced by unfocussed imaging. With Xrays, in particular, it is also possible to image the region 8 directlyby means of shadow projection.

The diaphragm shapes shown in FIGS. 3a to 3b have at least partiallyparabolic diaphragm apertures 9, 10 allowing light to pass through andshadow regions 11, 12. The diaphragm aperture 9 is enclosed by a rimformed of a straight line G₁ and a parabola P₁. The parabola P₁, whoseaxis of symmetry SY₁ is directed in the movement direction of therelative movement (Y' in the present case), connects two points S₁ andS₂ on the straight line G₁ normal to the movement direction.

The dose which can be achieved with this diaphragm is proportional tothe irradiation period t which, in turn, is dependent on the velocity vof the relative movement by which the region of the light beam 7 passingthrough the diaphragm aperture is moved along the surface to bestructured:

    t(X')=b(X')/v.

Quantity b is the aperture of the diaphragm in the movement directionwhich, in the present example, has the shape of parabola P₁. Theappropriate aperture of the diaphragm can be selected depending onapplication.

The aperture b, which is designated by b₁ for a location x₁, is thesecond quantity, besides velocity v, determining the dose acting on thesurface to be structured during the relative movement along the entiremovement path. Proceeding from a maximum dose value in the center of thediaphragm, the dose decreases to zero until the intersection of theparabola P₁ with the straight line G₁ at intersecting points S₁ and S₂.The dose profile which can be achieved with this diaphragm extends in adirection normal to the movement direction along the entire movementpath. A uniform and defined structure depth is ensured by temporal andspatial homogeneity of the light beam 7 and a constant velocity v.

The diaphragm shown in FIG. 3b has a rim formed of two parabolas P₂ andP₃ having a common axis of symmetry SY₂ directed in the movementdirection. Parabolas P₂ and P₃ are convex in the direction of movementand in the opposite direction and have common intersecting points S₃ andS₄ lying on a straight line G₂ normal to the movement direction. In thepresent example, the straight line G₂ does not form a rim. As in thepreceding construction, the two parabolas P₂ and P₃ can be asymmetricalbut also mirror-symmetrical.

The dose profiles which can be produced by the diaphragm according toFIG. 3b are identical to those formed by applying the diaphragmaccording to FIG. 3a. The advantage of the two-sided parabola shapeconsists in that it compensates for inaccuracies, in particular tilting.

The multiple diaphragm shown in FIG. 3c contains individual diaphragmswhich are arranged one after the other in the movement direction andhave diaphragm apertures 14 which correspond in shape to diaphragmaperture 9. In order to produce dose profiles with such multiplediaphragms it is sufficient to carry out the relative movement along apath length determined by the distances between the diaphragm apertures14. This results in a dose profile corresponding to cylindrical lensesarranged adjacent to one another in a parallel manner. When two exposureprocesses are carried out in directions at fight angles to one another,the dose profile corresponds to a lens array. It is possible to vary theconstruction of the multiple diaphragms with respect to the arrangement,shape and magnitude of the individual diaphragms.

For example, a multiple diaphragm can be so designed that withdimensions of 50×50 mm, 10,000 individual diaphragms in the shape ofdiaphragm apertures 14 with dimensions of 500 μm normal to the movementdirection and dimensions of a maximum of 250 μm in the movementdirection are provided. Exposure can be effected by shadow projectionwith colliding light. The use of X rays is also advantageous. Thesolution presents an inexpensive variant for producing giant arrays.

FIGS. 4 to 9 illustrate the results which can be obtained with differentdiaphragm shapes. Naturally, the invention is not limited to the shapeswhich are indicated here by way of example.

The figures designated by "a" indicate the diaphragm shape, while thosedesignated by "b" show the results obtained by applying these shapes inthe movement direction, and figures designated by "c" show the resultsobtained in the intersecting region of movement directions at fightangles to one another. The diaphragm according to FIG. 4a corresponds tothe diaphragm already described in FIG. 3a.

If a positive resist is used for the resist layer 5 as the surface to bestructured, a concave cylindrical lens according to FIG. 4b is formedwhen a region shaped by a parabolic diaphragm according to FIG. 4a ismoved relative to the surface and in the direction of the parabola aftera corresponding developing process.

When two exposure processes are carried out in directions oriented atright angles to one another, a radial concave lens can be produced,since a dose distribution corresponding to a lens of this type isproduced in the overlapping region of the two exposure processes (FIG.4c).

Elliptical lenses can also be produced by suitable selection ofdifferent diaphragm sizes.

The two exposure processes can also be effected using relative movementsin directions which are inclined relative to one another by anglesdiverging by 90°. This results in "displaced" variations of lenses. Thefocal lengths of the respective lens or components of the ellipticallens are determined by the velocity of the relative movement.

Convex cylindrical lenses according to FIG. 5b and radial convex lensesaccording to FIG. 5c can be realized with a diaphragm according to FIG.5a.

The diaphragm according to FIG. 5a has a diaphragm aperture 15corresponding to a portion which is left open in a rectangular rim 16 bya shadow element 17. Sides 18, 19 of a pair of sides of the rim aredirected normal to the movement direction. The side 19 coincides with astraight rim G₃ of the shadow element 17, the remaining rim of theshadow element 17 forming a parabola P₄ with an axis of symmetry SY₃ inthe movement direction connecting two points S₅ and S₆ on the straightrim G₃.

A diaphragm according to FIG. 6a with a diaphragm aperture 20 is usedfor fabricating Fresnel type lenses. When applied once in one movementdirection, a concave cylindrical Fresnel lens results. When two exposureprocesses are carried out in directions at right angles to one another,a concave Fresnel lens results, whose shape has already been describedin German Patent Application P 43 14 574.4.

A diaphragm of this type according to FIG. 6a is produced, as shown inFIG. 6d, in such a way that rectangular shadow elements R₁, R₂ sharing acommon side S₉, S₁₀ with the straight line G₄ are inserted in adiaphragm aperture 20' whose rim comprises a straight line G₄ and aparabola P₅ with intersecting points S₇, S₈. The sides S₁₁, S₁₂ locatedopposite sides S₉, S₁₀ contact the parabola P₅ by their end points, thisparabola P₅ having an axis of symmetry SY₄ which faces in the movementdirection. The portions A₁, A₂, A₃ which are left open form thediaphragm aperture 20 in that they are located at a common border G₅.

A diaphragm according to FIG. 7a provides convex Fresnel typecylindrical lenses or convex Fresnel lenses. Such lenses have alsoalready been described in German Patent Application P 43 14 574.4.

The diaphragm according to FIG. 7a has a diaphragm aperture 21 formed bya portion left open by a shadow element 23 in a rectangular rim 22,wherein a pair of sides of the rim 22 has sides 24, 25 in an orientationnormal to the movement direction.

According to FIG. 7d, the shadow element 23 is formed of partialelements E₁, E₂, E₃ which are left when at least one rectangular portionR₃, R₄ is removed from a surface enclosed by a straight line G₆ and aparabola P₆. The parabola P₆, whose axis of symmetry SY₅ is oriented inthe movement direction, connects two points S₁₃, S₁₄ on the straightline G₆ normal to the movement direction. While one side S₁₅, S₁₆ of therectangular portions R₃, R₄ coincides with straight line G₆, theopposite sides S₁₇, S₁₈ contact the parabola P₆ with their end points.In FIG. 7a, the partial elements form the diaphragm aperture 21 in thatthey are situated at side 25. It is also possible to use the other side24 for contact.

Another suitable diaphragm (FIG. 8a) can have a diaphragm aperture inthe shape of a right triangle 26, one of whose legs 27, 28 is directedin the movement direction.

FIG. 9a shows a diaphragm aperture 29 in the shape of an isoscelestriangle whose vertex formed by the equal sides is directed in themovement direction. Diaphragm aperture 26 results in corresponding wedgeprofiles, aperture 29 results in triangular and pyramidal profiles.

The diaphragms shown in FIGS. 10a and 10b are provided with adjustingslides 30 and 31 by means of which the diaphragm can be adjusted. Thebase width can be changed by adjusting slide 30, while the structurewidth can be changed by adjusting slide 31. Accordingly, lenses ofvarying geometry with respect to size can be produced in a simplemanner. Adjustment can be automated and can also be effected during anexposure process in order to vary the structure widths.

FIG. 11 illustrates the use of a multiple diaphragm as a beam shapingdevice. This solution corresponds to that shown in FIG. 2 with respectto function. Piezo-actuators (not shown) which are coupled to thediaphragm and produce easily controllable movements, e.g., in the formof oscillations, are suitable for carrying out the relative movement ofthe multiple diaphragm.

Dose profiles corresponding to round Fresnel lenses can be produced withthe arrangement which is shown schematically in FIG. 12. The diaphragmhas a corresponding diaphragm aperture 32. This solution corresponds tothat shown in FIG. 2 with respect to function, with the difference thatthe relative movement is produced by a rotational movement around axisZ--Z. FIG. 13 shows a round Fresnel lens produced in this way.

FIG. 14 illustrates the basic procedure for producing surface profileswith variable doses and thus shows an application for dose values whichcan be realized with the invention. While the resist layer 5 is beingdeveloped, a different irradiation intensity in the X-direction causes adevelopment front 33 which progresses with the duration of developmentand produces a surface profile in the resist.

Other applications are provided for radiation-sensitive objects in whichthe surface profile is developed into the object. Direct profiling ofthe object can also be effected by means of profile etching in that theradiation works the structure into the material directly, e.g., as inion-beam etching.

Cylindrical-lens arrays and lens arrays (FIG. 15b and FIG. 16b) can beproduced by the procedures of meandering exposure, as indicated by thearrows, shown in FIGS. 15 and 16.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the true spirit and scope of the presentinvention.

What is claimed is:
 1. In an arrangement for producing dose profiles for the fabrication of microlens arrays with a beam used for exposure and directed on a surface of a substrate, the improvement comprising:shaping means including a diaphragm assembly having a plurality of apertures for shaping the cross-section of a plurality of exposure beams, which shaping means generates a plurality of shaped beam cross-sections which are fixed relative to one another and movable relative to the surface and whose extents in the direction of the relative movement, in combination with the velocity of the relative movement, determines doses for a plurality of respective areas on said substrate, said apertures being arranged one behind the other in the direction of relative movement.
 2. The optical arrangement according to claim 1, wherein piezo-actuators are connected with the diaphragm assembly to produce the relative movement.
 3. The optical arrangement according to claim 2, wherein the relative movement corresponds to a distance between adjacent apertures of said diaphragm assembly in the movement direction.
 4. The optical arrangement according to claim 1, wherein at least one of the diaphragm apertures has a rim formed of a straight line and a parabola, said parabola having an axis of symmetry directed in the movement direction, which connects two points on a straight line normal to the movement direction.
 5. The optical arrangement according to claim 4, wherein at least one rectangular shadow element is placed in said one of the diaphragm apertures, one side of the rectangular shadow element coinciding with the straight line and the opposite side contacting the parabola by its end points.
 6. The optical arrangement according to claim 5, wherein the regions left open by the shadow element are situated at a common border by their edges which are in an orientation normal to the movement direction.
 7. The optical arrangement according to claim 1, wherein at least one of said diaphragm apertures has a rim formed of two parabolas, wherein the parabolas, which have a common axis of symmetry oriented in the movement direction, are constructed so as to be convex in the movement direction and opposite thereto and have common intersection points lying on a straight line normal to the movement direction.
 8. The optical arrangement according to claim 1, wherein at least one of the diaphragm apertures is a portion left open within a rectangular rim by a shadow element and wherein a pair of rim sides has sides extending in a direction normal to the movement direction.
 9. The optical arrangement according to claim 8, wherein one of the sides normal to the movement direction coincides with a straight rim of the shadow element, whose other rim is a parabola whose axis of symmetry in the movement direction connects two points on the straight rim.
 10. The optical arrangement according to claim 8, wherein the shadow element is formed of partial elements remaining after at least one rectangular portion is removed from a surface enclosed by a straight line and a parabola, wherein the parabola, whose axis of symmetry is oriented in the movement direction, connects two points on the straight line normal to the movement direction, one side of the rectangular portion coincides with the straight line, while the end points of the opposite side contact the parabola, and in that the partial elements are so disposed that their straight rims normal to the movement direction are located at one of the sides of the rectangular rim which are normal to the movement direction.
 11. The optical arrangement according to claim 1, wherein at least one of the apertures of the diaphragm assembly corresponds to a right triangle, one of whose legs is directed in the movement direction.
 12. The optical arrangement according to claim 1, wherein at least one of the apertures of the diaphragm assembly corresponds to an isosceles triangle whose vertex is formed by the equal sides is directed in the movement direction.
 13. The optical arrangement according to claim 1 wherein adjusting slides are provided for adjusting the shape or magnitude of the diaphragm assembly.
 14. The optical arrangement according to claim 1, wherein a display screen is used for shaping the cross sections of the beams. 